Current leakage mechanisms related to threading dislocations in Ge-rich SiGe heterostructures grown on Si(001)

This work investigates the role of threading dislocation densities (TDD) in the low density regime on the vertical transport in Si0.06Ge0.94 heterostructures integrated on Si(001). The use of unintentionally doped Si0.06Ge0.94 layers enables the study of the impact of grown-in threading dislocations (TD) without interaction with processing-induced defects originating, e.g., from dopant implantation. The studied heterolayers, while equal in composition, the degree of strain relaxation, and the thickness feature three different values for the TDD as 3 x 10(6), 9 x 10(6), and 2 x 10(7) cm(-2). Current-voltage measurements reveal that leakage currents do not scale linearly with TDD. The temperature dependence of the leakage currents suggests a strong contribution of field-enhanced carrier generation to the current transport with the trap-assisted tunneling via TD-induced defect states identified as the dominant transport mechanism at room temperature. At lower temperatures and at high electric fields, direct band-to-band tunneling without direct interactions with defect levels becomes the dominating type of transport. Leakage currents related to emission from mid-gap traps by the Shockley-Read-Hall (SRH) generation are observed at higher temperatures (> 100 & DEG;C). Here, we see a reduced contribution coming from SRH in our material, featuring the minimal TDD (3 x 10(6) cm(-2)), which we attribute to a reduction in point defect clusters trapped in the TD strain fields.